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Classification and external resources

A man with male pattern baldness
ICD-10 L65.9
ICD-9 704.0
DiseasesDB 14765
MeSH D000505

Baldness is the state of having no hair or lacking hair where it often grows, especially on the head. The most common form of baldness is a progressive hair thinning condition called androgenic alopecia or "male pattern baldness" that occurs in adult male humans and other species. The amount and patterns of baldness can vary greatly; it ranges from male and female pattern alopecia (androgenic alopecia, also called androgenetic alopecia or alopecia androgenetica), alopecia areata, which involves the loss of some of the hair from the head, and alopecia totalis, which involves the loss of all head hair, to the most extreme form, alopecia universalis, which involves the loss of all hair from the head and the body.


[edit] Signs and symptoms

The sign of baldness is a lack of hair on top of the persons head.

[edit] Cause

Incidence of pattern baldness varies from population to population based on genetic background, environmental factors do not seem to affect this type of baldness greatly. One large scale study in Maryborough, Victoria, Australia showed the prevalence of mid-frontal hair loss increases with age and affects 73.5% of men and 57% of woman aged 80 and over. According to Medem Medical Library's website, male pattern baldness affects roughly 40 million men in the United States. Approximately 25 percent of men begin balding by age 20; two-thirds begin balding by age 60. There is a 4 in 7 chance of getting the baldness gene.

Male pattern is characterized by hair receding from the lateral sides of the forehead, known as "receding hairline". Receding hairlines are usually seen in males above the ages of 20 but can be seen as early as late teens as well.

An additional bald patch may develop on top (vertex). The trigger for this type of baldness (called androgenetic alopecia) is DHT, a powerful sex hormone, body, and facial hair growth promoter that can adversely affect the prostate as well as the hair located on the head.[1]

The mechanism by which DHT accomplishes this is not yet fully understood. In genetically-prone scalps, DHT initiates a process of follicular miniaturization. Through the process of follicular miniaturization, hair shaft width is progressively decreased until scalp hair resembles fragile vellus hair or "peach fuzz" or else becomes non-existent. Onset of hair loss sometimes begins as early as end of puberty, and is mostly genetically determined. Male pattern baldness is classified on the Hamilton-Norwood scale I-VII.

It was previously believed that baldness was inherited from the maternal grandfather. While there is some basis for this belief, both parents contribute to their offspring's likelihood of hair loss. Most likely, inheritance is technically "autosomal dominant with mixed penetrance"[citation needed] (see 'baldness folklore' below)

There are several other kinds of baldness:

  • Traction alopecia is most commonly found in people with ponytails or cornrows who pull on their hair with excessive force.
  • Trichotillomania is the loss of hair caused by compulsive pulling and bending of the hairs. It tends to occur more in children than in adults. In this condition the hairs are not absent from the scalp but are broken. Where they break near the scalp they cause typical, short, "exclamation mark" hairs.
  • Traumas such as chemotherapy, childbirth, major surgery, poisoning, and severe stress may cause a hair loss condition known as telogen effluvium.[2] Hair follicles in the growing phase are affected by chemotherapy while this treatment targets dividing cancer cells. Therefore, almost 90% of hairs fall out soon after chemotherapy starts.[3]
  • Worrisome hair loss often follows childbirth without causing actual baldness. In this situation, the hair is actually thicker during pregnancy due to increased circulating oestrogens. After the baby is born, the oestrogen levels fall back to normal pre-pregnancy levels and the additional hair foliage drops out. A similar situation occurs in women taking the fertility-stimulating drug clomiphene.
  • Iron deficiency is a common cause of thinning of the hair, though frank baldness is not usually seen.
  • Radiation to the scalp, as happens when radiotherapy is applied to the head for the treatment of certain cancers there, can cause baldness of the irradiated areas.
  • Some mycotic infections can cause massive hair loss.[4]
  • Alopecia areata is an autoimmune disorder also known as "spot baldness" that can result in hair loss ranging from just one location (Alopecia areata monolocularis) to every hair on the entire body (Alopecia areata universalis).
  • Localized or diffuse hair loss may also occur in cicatricial alopecia (lupus erythematosus, lichen plano pilaris, folliculitis decalvans, central centrifugal cicatricial alopecia, postmenopausal frontal fibrosing alopecia, etc.). Tumours and skin outgrowths also induce localized baldness (sebaceous nevus, basal cell carcinoma, squamous cell carcinoma).
  • Hypothyroidism can cause hair loss, typically frontal, and is particularly associated with thinning of the outer third of the eyebrows (syphilis also can cause loss of the outer third of the eyebrows)
  • Hyperthyroidism can also cause hair loss, which is parietal rather than frontal.
  • Temporary loss of hair can occur in areas where sebaceous cysts are present for considerable duration; normally one to several weeks in length.
  • Congenital triangular alopecia ' It is a triangular, or oval in some cases, shaped patch of hair loss in the temple area of the scalp that occurs mostly in young children. The affected area mainly contains vellus hair follicles or no hair follicles at all, but it does not expand. Its causes are unknown and although it is a permanent condition, it does not have any other effect on the affected individuals.[5]

[edit] Evolutionary hypotheses

There is no consensus regarding the details of the evolution of male pattern baldness. The assertion that MPB is intended to convey a social message is supported by the fact that the distribution of androgen receptors in the scalp differs between men and women, and older men or women with high androgen levels often exhibit diffuse thinning of hair as opposed to male pattern baldness.

One hypothesis, advanced by Muscarella and Cunningham,[6] suggests baldness evolved in males through sexual selection as an enhanced signal of aging and social maturity, whereby aggression and risk-taking decrease and nurturing behaviours increase. This may have conveyed a male with enhanced social status but reduced physical threat, which could enhance ability to secure reproductive partners and raise offspring to adulthood.

In a study by Muscarella and Cunningham [6], males and females viewed 6 male models with different levels of facial hair (beard and mustache or none) and cranial hair (full head of hair, receding and bald). Participants rated each combination on 32 adjectives related to social perceptions. Males with facial hair and those with bald or receding hair were rated as being older than those who were clean-shaven or had a full head of hair. Beards and a full head of hair were seen as being more aggressive and less socially mature, and baldness was associated with more social maturity. A review of social perceptions of male pattern baldness has been provided by Henss (2001).[7]

Other evolutionary hypotheses include genetic linkage to beneficial traits unrelated to hair loss and genetic drift.

[edit] Non-human baldness

Baldness is not only a human trait. Some other primates, such as chimpanzees, stump-tailed macaques, and South American uakari show progressive thinning of the hair on the scalp after adolescence[citation needed]. Adult stump-tailed macaques, in fact, are commonly used in laboratories for the testing of hair-regrowth treatments.[citation needed]

The different predecessors of Old World and New World vultures convergently evolved a bald head, preventing feathers from retaining material from the vulture's diet of rotting meat, as well as helping in heat regulation.[8]

[edit] Genetics

Much research went into the genetic component of male pattern baldness, or androgenetic alopecia (AGA). Research indicates that susceptibility to premature male pattern baldness is largely X-linked. Other genes that are not sex linked are also involved.

German researchers name the androgen receptor gene as the cardinal prerequisite for balding.[9] They conclude that a certain variant of the androgen receptor is needed for AGA to develop. In the same year the results of this study were confirmed by other researchers.[10] This gene is recessive and a female would need two X chromosomes with the defect to show typical male pattern alopecia. Seeing that androgens and their interaction with the androgen receptor are the cause of AGA it seems logical that the androgen receptor gene plays an important part in its development.

Other research in 2007 suggests another gene on the X chromosome, that lies close to the androgen receptor gene, is an important gene in male pattern baldness. They found the region Xq11-q12 on the X-chromosome to be strongly associated with AGA in males. They point at the EDA2R gene as the gene that is mostly associated with AGA. This finding has been replicated in at least three following independent studies.

Other genes involved with hair loss have been found. One of them being a gene on chromosome 3. The gene is located at 3q26.[11] This gene is also involved in a type of baldness associated with mental retardation. This gene is recessive .

Another gene that might be involved in hair loss is the P2RY5. This gene is linked to hair structure. Certain variants can lead to baldness at birth while another variant causes "wooly hair".[12]

Recent research confirmed the X linked androgen receptor as the most important gene. With a gene on chromosome 20 being the second most important determinant gene (snpedia)

[edit] Female hair loss

Although baldness is not as common in women as in men, the psychological effects of hair loss tend to be much greater. Typically the frontal hairline is preserved but the density of hair is decreased on all areas of the scalp. Previously it was believed to be caused by testosterone just as in male baldness, but most women who lose hair have normal testosterone levels.[13]

However, female hair loss has become a growing problem which according to the American Academy of Dermatology affects around 30 million women in the United States. Although hair loss in females normally occurs after the age of 50 or even later when it does not follow events like pregnancy, chronic illness, crash diets, and stress among others, it is now occurring at earlier ages with reported cases in women as young as 15 or 16.[14]

Causes of female hair loss may vary from those that affect men. In the case of androgenic alopecia female hair loss occurs as a result of the action of androgens hormones (testosterone, androsteinedione, and dihydrotestosterone (DHT)). These male hormones normally occur in small amounts in women.

However, according to Ted Daly, MD, a dermatologist from Nassau University Medical Center on Long Island, androgenic alopecia is not the main cause of hair loss in women and dermatologists now prefer to call this condition female pattern hair loss instead of using the term androgenic alopecia. He adds that the female pattern is diffuse and goes around the whole top of the head and can affect women at any time.[15]

There are other instances in which the actions of hormones may also cause female hair loss. Some examples are: pregnancy, menopause, presence of ovarian cysts, birth control pills with a high androgen index, polycystic ovary syndrome. Also thyroid disorders, anemia, chronic illness and some medications can also cause female hair loss.[16]

[edit] Management

[edit] Psychological effects

Alopecia induced by cancer chemotherapy has been reported to cause changes in self-concept and body image. Body image does not return to the previous state after regrowth of hair for a majority of patients. In such cases, patients have difficulties expressing their feelings (alexithymia) and may be more prone to avoiding family conflicts. Family therapy can help families to cope with these psychological problems if they arise.[17]

Psychological problems due to baldness, if present, are typically most severe at the onset of symptoms.[18]

Some balding men may feel proud of their baldness, feeling a kindred relationship with famous charismatic bald men, such as Yul Brynner, Bruce Willis, Vin Diesel, Sean Connery, Jason Statham, Patrick Stewart, Ben Kingsley, "Stone Cold" Steve Austin, Tupac Shakur, Michael Chiklis, Telly Savalas, and Jeffrey Eugenides. Larry David specifically uses his baldness as a form of self-deprecating humor in his TV shows Seinfeld and Curb Your Enthusiasm . Baldness has, in recent years, become less of a liability due to an increasing fashionable prevalence of very short, or even completely shaven, hair among men in western countries. For instance, Patrick Stewart was called "The Sexiest Man on TV" for his charismatic role as Captain Jean-Luc Picard on Star Trek: The Next Generation.

Many companies have built a successful business selling products that reverse baldness, by allegedly regrowing hair, transplanting hair or selling hairpieces.

[edit] Preventing and reversing hair loss

Treatments for the various forms of alopecia have limited success. Some hair loss sufferers make use of clinically proven treatments such as finasteride, dutasteride and topically applied minoxidil solution, in an attempt to prevent further loss and regrow hair. As a general rule, it is easier to maintain remaining hair than it is to regrow; however, the treatments mentioned may prevent hair loss from Androgenetic alopecia, and there are new technologies in cosmetic transplant surgery and hair replacement systems that can be completely undetectable.

In the United States, there are only two drug-based treatments that have been approved by the U.S. Food and Drug Administration (FDA) and one product that has been cleared by the FDA for the treatment of androgenetic alopecia, otherwise known as male or female pattern hair loss. The two FDA approved treatments are finasteride (marketed for hair loss as Propecia) and minoxidil.

study that indicates a decline in free testosterone combined with an increase in strength due to an (unspecified) strength training regimen.[19]

[edit] Stress reduction

Stress reduction can be helpful in slowing hair loss.

[edit] Immunosuppressants

Immunosuppressants applied to the scalp have been shown to temporarily reverse alopecia areata, though the side effects of some of these drugs make such therapy questionable.[20][21]

[edit] Concealing hair loss

[edit] Head

One method of hiding hair loss is the "comb over", which involves restyling the remaining hair to cover the balding area. It is usually a temporary solution, useful only while the area of hair loss is small. As the hair loss increases, a comb over becomes less effective. When this reaches a stage of extreme effort with little effect'it can make the person the object of teasing or scorn.

Another method is to wear a hat or a hairpiece'a wig or toupee. The wig is a layer of artificial or natural hair made to resemble a typical hair style. In most cases the hair is artificial. Wigs vary widely in quality and cost. In the United States, the best wigs'those that look like real hair'cost up to tens of thousands of dollars. Organizations also collect individuals' donations of their own natural hair to be made into wigs for young cancer patients who have lost their hair due to chemotherapy or other cancer treatment in addition to any type of hair loss.

Lastly a number of alternative topical camouflages exist such as Nanogen (Europe) and Toppik (U.S.) and these are very popular as non-wig cosmetics which add electrostatic microfibres to your own hair.

[edit] Eyebrows

Though not as common as the loss of hair on the head, chemotherapy, hormone imbalance, forms of alopecia, and other factors can also cause loss of hair in the eyebrows. Artificial eyebrows are available to replace missing eyebrows or to cover patchy eyebrows. Micro tattooing is also available.

[edit] Embracing baldness

Instead of concealing hair loss, one may embrace it. A shaved head will grow stubble in the same manner and at the same rate as a shaved face. The general public has become accepting of the shaved head as well, but female baldness is less socially acceptable.

[edit] Society and culture

There are many myths regarding the possible causes of baldness and its relationship with one's virility, intelligence, ethnicity, job, social class, wealth etc. While skepticism is warranted due to lack of scientific validation, some of these myths may have a degree of underlying truth.

  • "You inherit baldness from your mother's father."
    • Previously, early baldness of the androgenic type was thought to be sex linked dominant in males and to be sex linked recessive in females.[citation needed]
    • Research suggests that the gene for the androgen receptor, which is significant in determining probability for hair loss, is located on the X chromosome and so is always inherited from the mother's side.[22] There is a 50% chance that a person shares the same X chromosome as their maternal grandfather. Because women have two X chromosomes, they will have two copies of the androgen receptor gene while men only have one. However, research has also shown that a person with a balding father also has a significantly greater chance of experiencing hair loss.[23][24]
  • "Intellectual activity or psychological problems can cause baldness."
    • This notion may be because cholesterol is involved in the process of neurogenesis and also the base material from which the body ultimately manufactures DHT. While the notion that bald men are more intelligent may lack credibility in the modern world, in the ancient world if a person was bald it was likely that he had an adequate amount of fat in his diet. Thus, his mental development was probably not stunted by malnutrition during his crucial formative years, he was more likely to be wealthy, and also have had access to a formal education. However, a sedentary lifestyle is less likely to correlate with intelligence in the modern world, and dietary fat content is not linked to economic class in modern developed countries. Another possibility is that, for some people, social standing accrued through intelligence can in mating compensate for physical attractiveness lowered by hair loss and therefore produce male offspring who are prone to both high intellect and hair loss. However, by way of better socioeconomic standing and in turn more access to hair loss treatments, an association between intelligence and actual hair loss is less likely in recent times. Of course, aside from all these scientific reasons, baldness could be linked to intellect or wisdom simply because people go bald as they age and become more experienced and less intelligent people tend to die younger.
    • Total testosterone exhibits a positive relation to tactual-spatial abilities and to the degree of lateralization. Total testosterone is negatively correlated with verbal fluency. Testosterone in the saliva is also significantly positively correlated to tactual-spatial test scores and, in addition, to field independence. DHT and the ratio DHT/total testosterone are positively related to verbal fluency and negatively to the degree of lateralization of tactual-spatial performance.[25]
  • "Baldness can be caused by emotional stress, sexual frustration etc."
    • Emotional stress has been shown to accelerate baldness in genetically susceptible individuals.[26]
    • Stress due to sleep deprivation in military recruits lowered testosterone levels, but is not noted to have affected SHBG.[27] Thus, stress due to sleep deprivation in fit males is unlikely to elevate DHT, which causes male pattern baldness. Whether it can cause hair loss by some other mechanism is not clear.
  • "Bald men are more 'virile' or sexually active than others."
    • Levels of free testosterone are strongly linked to libido and also DHT levels, but unless free testosterone is virtually non-existent levels have not been shown to affect virility. Men with androgenic alopecia are more likely to have a higher baseline of free androgens. However, sexual activity is multifactoral, and androgenic profile is also not the only determining factor in baldness. Additionally, because hair loss is progressive and free testosterone declines with age, a person's hairline may be more indicative of their past than present disposition.[28][29]
  • "Frequent ejaculation causes baldness"
    • There are many misconceptions about what can help prevent hairloss, one of these being that frequent ejaculation may have an influence on MPB. Depending on frequency, it can raise or lower plasma testosterone.[30]
  • "Standing on one's head alleviates baldness"
  • "Tight hats cause baldness."
    • While this may be a myth, hats do cause hair breakage and, to a lesser degree, split ends. Since hats are not washed as frequently as other clothing, they can also lead to scalp uncleanliness and possible Pityrosporum ovale contamination in men with naturally oily scalps. Some scalp infections, if left untreated, can cause hair loss.

[edit] Etymology

The term alopecia (pronounced /ˌæloÊŠˈpiːÊ�É�/) is formed from the Greek alópex (î�î»�Žπî�î�), meaning fox. The origin of this usage is because this animal sheds its coat twice a year.

The term bald likely derives from the English word balde, which means "white, pale", or Celtic ball, which means "white patch or blaze", such as on a horse's head.[31]

[edit] Research

Research is looking into connections between hair loss and other health issues. While there has been speculation about a connection between early-onset androgenetic alopecia and heart disease, a review of articles from 1954 to 1999 found no conclusive connection between baldness and coronary artery disease. The dermatologists who conducted the review suggested further study was needed.[32]

Environmental factors are under review. A 2007 study indicated that smoking may be a factor associated with age-related hair loss among Asian men. The study controlled for age and family history, and found statistically significant positive associations between moderate or severe androgenetic alopecia and smoking status.[33]

In May 2007, researchers at the University of Pennsylvania unveiled a new scientific breakthrough that may cure baldness with stem cells. A product could be on the market within three years.[34][35] The researchers discovered that the growth of new hair producing follicles could be stimulated in mice by damaging their skin.[36]

In February 2008 researchers at the University of Bonn announced they have found the genetic basis of two distinct forms of inherited hair loss, opening a broad path to treatments for baldness. The fact that any receptor plays a specific role in hair growth was previously unknown to scientists and with this new knowledge a focus on finding more of these genes may be able to lead to therapies for very different types of hair loss.[37][38]

An eight month study performed at the School of Pharmaceutical Sciences at the University of Science Malaysia showed daily supplements of a patented tocotrienol (vitamin E) complex may increase hair growth in people with male pattern baldness by 42 percent.[39]

In May 2009, researchers in Japan identified a gene, SOX21, that appears to be responsible for hair loss in people.[40]

[edit] See also

[edit] References

  1. ^ Rebora A (2004). "Pathogenesis of androgenetic alopecia". J Am Acad Dermatol 50 (5): 777'9. doi:10.1016/j.jaad.2003.11.073. PMID 15097964. 
  2. ^ Nnoruka E, Nnoruka N (October 2005). "Hair loss: is there a relationship with hair care practices in Nigeria?". Int J Dermatol 44 (Suppl 1): 13'7. doi:10.1111/j.1365-4632.2005.02801.x. PMID 16187950. 
  3. ^ "Anagen Effluvium". http://americanhairloss.org/women_hair_loss/causes_of_hair_loss.asp. Retrieved 2010-06-29. 
  4. ^ Pappas P, Kauffman C, Perfect J, Johnson P, McKinsey D, Bamberger D, Hamill R, Sharkey P, Chapman S, Sobel J (1995). "Alopecia associated with fluconazole therapy.". Ann Intern Med 123 (5): 354'7. PMID 7625624. 
  5. ^ "Congenital triangular alopecia". http://www.keratin.com/af/af005.shtml. Retrieved 2010-06-29. 
  6. ^ a b Muscarella, F. & Cunningham, M.R. (1996). "The evolutionary significance and social perception of male pattern baldness and facial hair.". Ethology and Sociobiology 17 (2): 99'117. doi:10.1016/0162-3095(95)00130-1. 
  7. ^ Henss, R. (2001). "Social perceptions of male pattern baldness. A review". Dermatology and Psychosomatics 2 (1): 63'71. doi:10.1159/000049641. 
  8. ^ Stanley Rice (September 1987). "On the Problem of Apparent Evil in the Natural World". Perspectives on Science and Christian Faith 39: 150'157. http://www.asa3.org/ASA/PSCF/1987/PSCF9-87Rice.html. 
  9. ^ Hillmer AM, Hanneken S, Genetic variation in the human androgen receptor gene is the major determinant of common early-onset Androgenetic Alopecia (AGA). Department of Genomics, Life and Brain Center, University of Bonn, Bonn, Germany.
  10. ^ Levy-Nissenbaum E, Bar-Natan M, Confirmation of the association between male pattern baldness and the androgen receptor genr Danek Gartner Institute of Human Genetics, Sheba Medical Center, Tel Hashomer, Israel
  11. ^ Hillmer AM, Flaquer A, Genome-wide scan and fine-mapping linkage study of AGA reveals a locus on chromosome 3q26. Department of Genomics, Life and Brain Center, University of Bonn, D-53127 Bonn, Germany.
  12. ^ Petukhova L, Sousa EC Jr, Martinez-Mir A, Vitebsky A, Dos Santos LG, Shapiro L, Haynes C, Gordon D, Shimomura Y, Christiano AM. Genome-wide linkage analysis of an autosomal recessive hypotrichosis identifies a novel P2RY5 mutation. Genomics. 2008 Nov;92(5):273'8. Epub 2008 Sep 13. PubMed PMID: 18692127.
  13. ^ Birch MP, Lalla SC, Messenger AG (July 2002). "Female pattern hair loss". Clin. Exp. Dermatol. 27 (5): 383'88. doi:10.1046/j.1365-2230.2002.01085.x. PMID 12190638. http://www3.interscience.wiley.com/resolve/openurl?genre=article&sid=nlm:pubmed&issn=0307-6938&date=2002&volume=27&issue=5&spage=383. 
  14. ^ "Women and Hair Loss: The Causes". http://www.webmd.com/skin-problems-and-treatments/hair-loss/features/women-hair-loss-causes. Retrieved 2010-06-29. 
  15. ^ "Female, Male Balding Not the Same Pattern". http://www.webmd.com/skin-problems-and-treatments/hair-loss/features/women-hair-loss-causes?page=2. Retrieved 2010-06-29. 
  16. ^ "Andogenetic Alopecia". http://americanhairloss.org/women_hair_loss/causes_of_hair_loss.asp. Retrieved 2010-06-29. 
  17. ^ Poot F (2004). "[Psychological consequences of chronic hair diseases]". Rev Med Brux 25 (4): A286'8. PMID 15516058. 
  18. ^ Passchier J, Erdman J, Hammiche F, Erdman R (2006). "Androgenetic alopecia: stress of discovery.". Psychol Rep 98 (1): 226'8. doi:10.2466/PR0.98.1.226-228. PMID 16673981. 
  19. ^ Ara, I.; Perez-Gomez, J.; Vicente-Rodriguez, G.; Chavarren, J.; Dorado, C.; Calbet, J. A. L. (2006). "Serum free testosterone, leptin and soluble leptin receptor changes in a 6-week strength-training programme." ([dead link]). British Journal of Nutrition 96 (6): 1053'9. doi:10.1017/BJN20061956. PMID 17181880. http://www.ingentaconnect.com/content/cabi/bjn/2006/00000096/00000006/art00009. 
  20. ^ Joly P (October 2006). "The use of methotrexate alone or in combination with low doses of oral corticosteroids in the treatment of alopecia totalis or universalis". J Am Acad Dermatol. 55 (4): 632'6. doi:10.1016/j.jaad.2005.09.010. PMID 17010743. 
  21. ^ Freyschmidt-Paul P, Ziegler A, McElwee KJ, et al. (2001). "Treatment of alopecia areata in C3H/HeJ mice with the topical immunosuppressant FK506 (Tacrolimus)". Eur J Dermatol 11 (5): 405'9. PMID 11525945. http://www.john-libbey-eurotext.fr/medline.md?issn=1167-1122&vol=11&iss=5&page=405. 
  22. ^ Hillmer A, Hanneken S, Ritzmann S, Becker T, Freudenberg J, Brockschmidt F, Flaquer A, Freudenberg-Hua Y, Jamra R, Metzen C, Heyn U, Schweiger N, Betz R, Blaumeiser B, Hampe J, Schreiber S, Schulze T, Hennies H, Schumacher J, Propping P, Ruzicka T, Cichon S, Wienker T, Kruse R, Nothen M (2005). "Genetic variation in the human androgen receptor gene is the major determinant of common early-onset androgenetic alopecia.". Am J Hum Genet 77 (1): 140'8. doi:10.1086/431425. PMID 15902657. 
  23. ^ Chumlea W, Rhodes T, Girman C, Johnson-Levonas A, Lilly F, Wu R, Guo S (2004). "Family history and risk of hair loss.". Dermatology 209 (1): 33'9. doi:10.1159/000078584. PMID 15237265. 
  24. ^ Genetics of Pattern Baldness
  25. ^ Christiansen K (1993). "Sex hormone-related variations of cognitive performance in !Kung San hunter-gatherers of Namibia.". Neuropsychobiology 27 (2): 97'107. doi:10.1159/000118961. PMID 8515835. 
  26. ^ Schmidt J (1994). "Hormonal basis of male and female androgenic alopecia: clinical relevance.". Skin Pharmacol 7 (1-2): 61'6. doi:10.1159/000211275. PMID 8003325. 
  27. ^ Remes K, Kuoppasalmi K, Adlercreutz H (1985). "Effect of physical exercise and sleep deprivation on plasma androgen levels: modifying effect of physical fitness.". Int J Sports Med 6 (3): 131'5. doi:10.1055/s-2008-1025825. PMID 4040893. 
  28. ^ Toone B, Wheeler M, Nanjee M, Fenwick P, Grant R (1983). "Sex hormones, sexual activity and plasma anticonvulsant levels in male epileptics.". J Neurol Neurosurg Psychiatry 46 (9): 824'6. doi:10.1136/jnnp.46.9.824. PMID 6413659. 
  29. ^ Davidson J, Kwan M, Greenleaf W (1982). "Hormonal replacement and sexuality in men.". Clin Endocrinol Metab 11 (3): 599'623. doi:10.1016/S0300-595X(82)80003-0. PMID 6814798. 
  30. ^ Exton MS, Krüger TH, Bursch N, et al. (November 2001). "Endocrine response to masturbation-induced orgasm in healthy men following a 3-week sexual abstinence". World J Urol 19 (5): 377'82. doi:10.1007/s003450100222. PMID 11760788. http://link.springer.de/link/service/journals/00345/bibs/1019005/10190377.htm. 
  31. ^ Harper, Douglas. "Entry for "bald"". Online Etymology Dictionary. http://www.etymonline.com/index.php?term=bald. Retrieved 2006-12-07. 
  32. ^ Rebora A (1 July 2001). "Baldness and coronary artery disease: the dermatologic point of view of a controversial issue". Arch Dermatol 137 (7): 943'7. PMID 11453815. http://archderm.ama-assn.org/cgi/pmidlookup?view=long&pmid=11453815. 
  33. ^ Asian men who smoke may have increased risk for hair loss
    Su LH, Chen TH (November 2007). "Association of androgenetic alopecia with smoking and its prevalence among Asian men: a community-based survey". Arch Dermatol 143 (11): 1401'6. doi:10.1001/archderm.143.11.1401. PMID 18025364. 
  34. ^ [1]
  35. ^ [2]
  36. ^ Berman, Jessica (17 May 2007). "Scientists Grow New Hair in Mice". VOA News (Voice of America). http://voanews.com/english/archive/2007-05/2007-05-17-voa63.cfm. Retrieved 5 January 2009. 
  37. ^ [3]
  38. ^ [4]
  39. ^ [5]
  40. ^ [6]

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